abstract = "In this research, a novel analysis technique for
impedance spectroscopy (IS) measurements is introduced
and applied to the investigation of symmetric cells. IS
is a powerful and non destructive method of
characterizing electrical properties of materials. The
analysis program is based on genetic programming (GP)
which is an evolutionary-based optimization algorithm.
The GP computing approach allows the evolutions of both
the model and the numerical parameters of a certain
model based on its fitness to a general mathematical
problem. In contrast to the conventional analysis
methods used for impedance spectroscopy measurements,
e.g. equivalent circuits, our program seeks the
distribution of relaxation times, DFRT, that has the
form of a peak or a sum of several peaks, assuming the
Debye kernel. Using this method one finds a functional
(parametric) form of the distribution of relaxation
times. By finding a functional form of the DFRT, one
may develop a physical model and examine its
behavior.

This analysis technique is used to investigate the
oxygen reduction reaction at the cathode side of solid
oxide fuel cells (SOFC). Two symmetric cell
configurations (SCC) where chosen : (i) The first
configuration is composed of Pt│GDC│Pt, where the
Pt layer serves as cathode material as well as current
collector; GDC is the electrolyte material. (ii) The
Second configuration is composed of
Pt│LSCF│GDC│LSCF│Pt, where LSCF serves as the
electrode material. IS measurements combined with I-V
measurements were employed on several samples at
several temperatures and several oxygen partial
pressures in order to investigate their influence on
the oxygen reduction reaction.

The resulting IS data was analyzed using the ISGP
program and the resulting peaks constructing the DFRTs
were assigned for different processes that occur at the
cathode side. The activation energies as well as the
dependence of the processes on the oxygen partial
pressure were also evaluated. The polarization curves
obtained were analyzed using the Butler-Volmer (B-V)
relations and a proposed model was suggested for the
behavior of the examined cell.",

notes = "March 2017: Access is available only to users in the
Technion Campus premises. Supervisors Tsur Yoed and
Sioma Baltianski",